Patent GB-553230-A (GB)
Title: Improvements in and relating to colour photography
IPC: G03C7/18
Filed: 1941-07-25
Abstract: 553,230. Colour photography. KODAK, Ltd., and BRANCH, L. E. T. July 25, 1941, Nos. 10435/42 and 10436/42, [both divided out of 553,196]. Drawings to Specification. [Class 98 (ii)] In the subtractive reproduction of a multicoloured original by a photographic or photomechanical process, colour correction is effected by making three-colour-component records from the original, by contact or projection printing on one support or on separate supports, while it is in register with a mask having a single image which, in order to compensate for the undesired light absorption of lights of two primary colours by one colour-component record is either (a) a red component record coloured with a mixture of minus blue and minus green, or (b) a green component record coloured with a mixture of minus blue and minus red, or (c) a red-andgreen component record coloured with a mixture of minus blue and minus green, or (d) a record as in (c) but coloured with a mixture of minus blue and minus red; or alternatively, while it is in register with a mask having a single image which, in order to compensate for the undesired light absorption of blue light and either red light or green light by a component record coloured minus green or minus red, and also in order to compensate for the undesired light absorption of green light by the component record coloured minus red or of red light by the component record coloured minus green, is a red-and-green component record coloured with a mixture of minus blue, minus green and minus red. The masking image is not formed in a sensitive layer in which a colour component picture record is made, although it may be formed, e.g. as described in Specification 547,519, in a layer integral with a layer or layers containing colour component picture records. The absorption gamma or gammas of the mask, measured by light of a colour or colour undesirably absorbed, must bear a certain relation or relations, which are set out in detail in the Specification, to the absorption gamma or gammas, similarly measured, of the component colour image or images which exhibit the undesired absorption or absorptions. Mask (a) compensates for blue and green light absorption by the cyan image, mask (b) for blue and red light absorption by the magenta image, mask (c) for blue light absorption by the magenta and cyan images and for green light absorption by the cyan image, and mask (d) for blue light absorption by the magenta and cyan images and for red light absorption by the magenta image. The correcting process may be extended by using in the reproduction a mask having two images, e.g. in superimposed layers on a single support or in a mixed grain emulsion layer, one of which is as defined at (a) above and the other of which is either a green component record coloured minus blue to compensate also for the blue light absorption of the' magenta image, or a green component record coloured minus red to compensate also for the red light absorption of the magenta image ; or alternatively, one of which is as defined at (b) above, and the other of which is either a red component record coloured minus blue to compensate also for the blue light absorption of the cyan image, or a red component record coloured minus green to compensate also for the green light absorption of the cyan image ; or alternatively again, one of which is as defined at (a) above and the other as defined at (b) above. Directions are also given in the Specification regarding the absorption gammas of these doubleimage masks. The correction may be directed towards compensating for the undesired lightabsorption of the dyestuffs to be used in the copy, or of those used in the original if this is itself a multicolour reproduction, or of both, the gamma of the mask in the last-mentioned case being appropriately raised. The masking images may be coloured by direct or indirect colour development, the developer silver being removed. The colour of the masking image may be adjusted to compensate for incorrectness of the gamma of one of the records, e.g. the effective contrast of the cyan image may be reduced by including in mask (a) a proportion of cyan ; and in this case the mask may be made by colour development of a single emulsion, using a mixture of colour couplers of the same kind as those used in producing the original or the copy. A formula is given for an orange colour developer made by mixing with a solution -containing 2-amino-5- diethylaminotoluene, sodium sulphite and potassium thiocyanate, a solution containing acetoacetp-nitro-anilide and sodium hydroxide. Specifications 427,516, 427,518, 427,520, 458,665, 478,942, 493,952, 494,341, 512,608, 517,416, 537,864 and 551,614, also are referred to.